Embodiments of the present disclosure relate to fuel vapor processing apparatus that may include a canister for adsorbing fuel vapor generated in a fuel tank, a closing valve provided in a vapor passage connecting the canister and the fuel tank to each other, and a purge passage connecting the canister and the intake passage of an engine.
JP-A-2005-155323 discloses a fuel vapor processing apparatus that may include a canister for adsorbing fuel vapor generated in a fuel tank, a closing valve provided in a vapor passage connecting the canister and the fuel tank to each other, and a purge passage connecting the canister and the intake passage of an engine.
In the fuel vapor processing apparatus of this document, if a predetermined purge condition is satisfied after driving of the engine, the interior of the canister may be brought to communicate with the atmosphere. In this state, the intake negative pressure of the engine may be applied to the interior of the canister via the purge passage. As a result, the atmospheric air may flow into the canister to desorb the fuel vapor adsorbed by the adsorbent. The fuel vapor desorbed from the adsorbent may be introduced into the engine via the purge passage. Further, while the purge operation is performed for the canister, the closing valve of the vapor passage may be opened for a depressurization control of the fuel tank.
Here, the closing valve used in the fuel vapor processing apparatus may be opened when an ON-signal is received from an ECU and may be closed when an OFF-signal is received from the ECU. A duty ratio control may be performed on the ON-signal and the OFF-signal from the ECU, whereby the flow rate of the gas flowing through the closing valve is adjusted for the depressurization control of the fuel tank.
In the above-described fuel vapor processing apparatus, the flow rate (depressurization flow rate) of the gas flowing through the closing valve is adjusted under the duty ratio control, whereby the depressurization control is performed for the fuel tank. However, due to the duty ratio control, the closing valve is periodically turned ON and OFF to periodically repeat the fully opened state and the fully closed state of the valve in order to adjust the average flow rate per unit time of the gas flowing through the closing valve. Therefore, it is difficult to perform fine adjustment of the flow rate. As a result, the depressurization control may not be accurately performed.
Therefore, there has been a need in the art for making it possible to accurately perform a depressurization control for the fuel tank.